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Date: Wed, 5 Jul 2006 02:31:20 -0700
From: Andrew Morton <akpm@osdl.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: torvalds@osdl.org, linux-kernel@vger.kernel.org, arjan@infradead.org
Subject: Re: [patch] uninline init_waitqueue_*() functions
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In-Reply-To: <20060705084914.GA8798@elte.hu>
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On Wed, 5 Jul 2006 10:49:14 +0200
Ingo Molnar <mingo@elte.hu> wrote:

> Subject: uninline init_waitqueue_*() functions
> From: Ingo Molnar <mingo@elte.hu>
> 
> some wait.h inlines are way too large: init_waitqueue_entry() and
> init_waitqueue_func_entry() generate 20-30 bytes of inlined code
> per call site, and init_waitqueue_head() is 30-40 bytes (on x86).

20-30 bytes for

> -static inline void init_waitqueue_entry(wait_queue_t *q, struct task_struct *p)
> -{
> -	q->flags = 0;
> -	q->private = p;
> -	q->func = default_wake_function;
> -}

seem too much.

This:

--- a/fs/select.c~a
+++ a/fs/select.c
@@ -129,6 +129,7 @@ static void __pollwait(struct file *filp
 	entry->filp = filp;
 	entry->wait_address = wait_address;
 	init_waitqueue_entry(&entry->wait, current);
+	init_waitqueue_entry(&entry->wait, current);
 	add_wait_queue(wait_address,&entry->wait);
 }
 

Increases fs/select.o by only seven bytes.


And this:

diff -puN fs/select.c~a fs/select.c
--- a/fs/select.c~a
+++ a/fs/select.c
@@ -128,7 +128,7 @@ static void __pollwait(struct file *filp
 	get_file(filp);
 	entry->filp = filp;
 	entry->wait_address = wait_address;
-	init_waitqueue_entry(&entry->wait, current);
+	xxinit_waitqueue_entry(&entry->wait, current);
 	add_wait_queue(wait_address,&entry->wait);
 }
 
_

shrinks fs/select.o by eight bytes.  (More than I expected).  So it does
appear to be a space win, but a pretty slim one.